Lithium ion cells generally utilize two different insertion compounds as host cathode and anode materials, i.e., intercalation materials, for the reversible insertion of guest ions (e.g. lithium ions, or other alkaline metal ions) in providing the electrochemical reactions for generation of an electrical current. During discharge of a lithium ion cell, lithium ions are extracted from the lithium ion containing anode material and are ionically transported through the electrolyte/separator into the cathode, with generation of an external electrical current. The reverse process occurs on charging of the cell with reversal of ion flow.
Lithium ion cells may either be conventional liquid electrolyte based cells, i.e., with free liquids, generally of a non-aqueous organic nature, or can be "solid state" cells having a polymeric porous matrix in which the electrolyte is immobilized. The polymeric matrix comprises a porous separator between anode and cathode to permit the requisite ionic transport between anode and cathode. In a solid state rechargeable, or "secondary" cell system, lithium (or other electrochemically active metal) is shuttled back and forth between the cathode and anode in the form of ions dissolved in the non-aqueous electrolyte (whether free or immobilized in a polymeric matrix).
Because of electrolyte immobilization in polymer cells, a necessary function of cell construction, safety and dimensional flexibility; there is a reduction in ion transport rate. This may result in deterioration in both cell discharge capability and recycling efficiency, particularly under conditions of use after elevated temperature storage conditions.
Various expedients have been utilized, particularly in the form of electronic and ion transport enhancing additives and stabilizers being included in the various cell components and particularly the anode and electrolyte. However, these expedients have been only minimally effective. It is believed that other factors, aside from ionic and electronic conductivity are involved in deterioration of cell performance which the prior art expedients have not effectively addressed.